The folded dipole antenna of the present invention was developed to overcome certain deficiencies in existing antenna systems. This antenna has an extremely broad bandwidth in the high frequency ranges (1.8-30 MHz) and can maintain effective radiated power using a shorter antenna span.
Most present day users of antennas for communication purposes desire an antenna to operate on multiple frequencies without having to resort to antenna tuning devices. Most antennas require tuning devices which are usually placed between the radio frequency transmitter and the antenna to properly tune the antenna to match the desired broadcast frequency. Another requirement, or rather a problem, is that the antenna must be capable of fitting into the space available. In many instances, such as roof top installations, the space available is quite short and will not be able to accommodate antennas of extreme overall length. Further, in various localities, e.g. foreign countries, frequency allocations can be changed without prior notice. This would put the user virtually in a position where he can no longer operate his communications facility.
In the past, trap dipole antennas have been used to alleviate some of the above conditions and problems. The use of the trap dipole antennas has resulted in somewhat poor to unsatisfactory operating conditions of the communications systems because of narrow bandwidths typical to this type of antenna. In many cases the user requires a preassembled antenna for use on certain frequencies. However, due to differing conditions at the point of installation, i.e. height above ground, ground conditions, surrounding objects, etc., it is not always possible to preassemble an antenna in a factory which will work effectively in all desired locations.
The trap-type antennas were designed to be able to receive and transmit over certain designated frequencies selected by the user. This was accomplished by creating artificial antenna electrical lengths shorter than the entire length of the antenna so that the antenna would look either shorter or longer to the radio frequency generator. This enabled the user to transmit or receive over certain frequencies located at selected points along the frequency spectrum. However, this limited the user to only those specific frequencies because of the narrow bandwidths of this type antenna. The trap-type antenna was not capable of operating over its entire frequency range.
Antenna tuning devices have also been used to assist trap-type antennas to attain certain frequencies in adverse environmental conditions. This is because the traps will vary in frequency due to temperature, humidity and other environmental conditions. Therefore, a trap-type antenna which has been designed for operation on certain frequencies and preassembled in a factory will, even though tuned for specific frequencies, change considerably once it is installed at its location. The frequency changes will then necessitate the use of an antenna tuning device which may or may not be capable of bringing the antenna back to the desired characteristics.